The purposes of the study are (1) Assess the effectiveness of chronic electrical stimulation of midbrain sites for the relief of chronic pain in humans; (2) Evaluate the efficacy and mechanisms of traditional narcotic analgesia and compare these to chronic electrical stimulation of midbrain sites; (3) Validate experimental models of pain and their potential diagnostic use in chronic pain patients; and (4) Determine and compare the impact of both traditional natcotic and chronic lectrical stimulation therapies on the functional, intellectual and emotional well being of these patients. The effects of chronic brain stimulation in surgical patients will be compared to the effects of narcotics previously administered to patients and to effects of narcotic regimes in non- surgical chronic pain patients. In addition, the effects of narcotics on perceptual and neural mechanisms of experimental induced pain we be assessed in pain-free volunteers. A follow-up of one patient supports previous findings from this project. This patient, who received an implantable stimulator in April 1986, reported moderate pain relief in a postoperative visit to the NIH in May 1986. He presently attributes minimal pain relief to his stimulator, and provides evidence that his previously reported relief may reflect an ambitious exercise program and not the effects of stimulation. These findings are consistent with previous results of this project. Analgesia from deep brain stimulation is not opioid mediated, is less potent than morphine nalgesia and follows a longer time course than analgesia following narcotic administrations.